With mass application of new services such as multimedia and cloud computing, communication traffic double increases each year and users have increasingly high requirements for bandwidth. To meet requirements for fast network capacity increase and low latency, optical switching starts to be used in networks gradually. When an optical packet switching node in an optical packet switching system runs for a long time, some internal switch units of a core optical packet switch in the optical packet switching system deteriorate in performance due to reasons such as aging, and consequently, some links between an input port and an output port of the optical packet switch fail, and some optical packets cannot be switched to a correct output port. Therefore, in an optical switching process, it is necessary to determine whether a switching link corresponding to an optical packet is normal.
Currently, a circulator is added at each input port and each output port of an optical packet switch to implement that a test signal generated by a link determining device passes through the optical switch and returns to the link determining device. Specifically, first, the link determining device generates N different test signals, and couples these test signals to a circulator on an output side of the optical packet switch; then a circulator on an input side of the optical packet switch separates the test signals from an input signal, and transmits the test signals to the link determining device; and finally the link determining device compares the received test signals with an expected test signal to determine whether a corresponding switching link is normal.
However, if a circulator is added at each input port and each output port of the optical packet switch, a corresponding circulator needs to be added at each input port and each output port of the optical packet switch, and therefore, a large quantity of circulators are needed in the optical packet switching apparatus, which causes relatively high optical packet switching costs.